The present invention relates to a control system of an engine, particularly to a control system of an engine, which controls, by using a tumble flow, a behavior of fuel which is directly injected into a combustion chamber formed inside a cylinder of the engine.
In accordance with recent tightening of the exhaust gas restriction for automobiles, there has been a strong demand for improvement of fuel consumption as well as a purifying performance of exhaust gas discharged from an engine.
In exhaust paths of the automobiles, a redox catalyst for purifying unburned gas (e.g., HC, CO, and NOx) contained within the exhaust gas of the engine is provided. In order to purify the unburned gas by this catalyst, it is necessary to maintain a temperature of the catalyst at its activating temperature or above.
Therefore, if a temperature of the exhaust gas is low and the temperature of the catalyst has not reached the activating temperature, which is the case, for example, immediately after a cold start of the engine, the temperature of the catalyst needs to be increased promptly so as to secure the purifying performance of the exhaust gas.
Therefore, retarding an ignition timing to after a top dead center on compression stroke (CTDC) immediately after the cold start in which the temperature of the catalyst is low, so as to cause high-temperature exhaust gas to flow into the catalyst and increase the temperature thereof, has been discussed. However, in this case, the retarding of the ignition timing to after the CTDC causes a temperature and pressure drop inside a combustion chamber of the engine, and thus, ignition stability degrades and even if the ignition can be performed successfully, flame propagation becomes poor. Therefore, with a spark-ignition direct-injection engine disclosed in JP2010-150971A, in a cold state of the engine, fuel is injected in two injections on intake stroke and in a latter half of compression stroke, and the fuel for the latter half of the compression stroke is injected to collide with a top surface and/or a cavity of a piston of the engine. Thus, a rich atmosphere is formed around the ignition plug at the ignition timing, and the ignition stability and the flame propagation (combustion stability) are improved.
However, with the conventional spark-ignition direct-injection engine described above, when the fuel injected in the latter half of the compression stroke collides with the top surface and/or the cavity of the piston, part of the fuel adheres to the piston. Such fuel adhesion to the piston degrades the fuel consumption and also increases smoke and hydrocarbons (HC) (unburned gas) contained within the exhaust gas, which degrades emission performance.
Further, if a fuel injection amount in the latter half of the compression stroke is reduced to suppress the fuel adhesion to the piston, the rich atmosphere cannot sufficiently be formed around the ignition plug at the ignition timing after the CTDC, and the combustion stability degrades.